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Devonian of the Franlinian Eugeosyncline
The magmatic belt of the Franklinian geosyncline, represented by the lower Palaeozoic and Proterozoic rocks of northern Axel Heiberg and Ellesmere Islands, differs in depositional and tectonic history from the “miogeosyncline” in the south.
Devonian sedimentary and volcanic strata are confined to northern Axel Heiberg Island; granitic intrusions occur on both Axel Heiberg and Ellesmere Islands.
The red weathering Lower Devonian Stallworthy Formation comprising about 12,000 feet of quartz-chert arenite, siltstone, conglomerate, shale, and minor tuff indicates non-marine and deltaic environments. Resting unconformably upon late Wen-lockian strata, it is a post-tectonic deposit related to movements that began in the Wenlockian, and probably culminated in the early Ludlovian.
The Stallworthy is conformably overlain by the Svartevaeg Formation, about 10,400 feet of graded volcanic arenite and siltstone with keratophyre, spilite, basalt, conglomerate, breccia, and shale. The conglomerates and breccias are submarine slides, and inlude Silurian carbonates; the arenites and siltstones are turbidites. The formation, tentatively considered as Middle Devonian, suggests a sudden down-warping which probably preceded a major orogeny culminating in granitic intrusions.
The intrusions comprise numerous small, high-level plutons of quartz diorite, quartz monzonite, granodiorite, diorite, etc., and at least one stock indicative of greater depth. The youngest known strata intruded are Lower Silurian, but a K-Ar age determination suggests emplacement 360 ± 25 m.y. ago, i.e. probably in the late Middle or Late Devonian, just piror to, or contemporaneously with a major uplift of the northernmost regions that produced a thick Upper Devonian clastic wedge in the south.
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